[layouts] Avoid rasterizing the whole layout when only a single item has opacity set

Instead, only rasterize that one item and pre-apply it's opacity
to the rasterized version. This keeps all the rest of the layout
content as vectors/text.

python/core/auto_generated/layout/qgslayoutitem.sip.in

@@ -238,6 +238,13 @@ Base class for graphical items within a :py:class:`QgsLayout`.
       UndoCustomCommand,
     };
 
+    enum Flag
+    {
+      FlagOverridesPaint,
+    };
+    typedef QFlags<QgsLayoutItem::Flag> Flags;
+
+
     explicit QgsLayoutItem( QgsLayout *layout, bool manageZValue = true );
 %Docstring
 Constructor for QgsLayoutItem, with the specified parent ``layout``.
@@ -279,6 +286,13 @@ upon creation.
 .. seealso:: :py:func:`id`
 
 .. seealso:: :py:func:`setId`
+%End
+
+    virtual Flags itemFlags() const;
+%Docstring
+Returns the item's flags, which indicate how the item behaves.
+
+.. versionadded:: 3.4.3
 %End
 
     QString id() const;
@@ -1166,6 +1180,9 @@ Applies any present data defined size overrides to the specified layout ``size``
 
 };
 
+QFlags<QgsLayoutItem::Flag> operator|(QgsLayoutItem::Flag f1, QFlags<QgsLayoutItem::Flag> f2);
+
+
 
 
 

python/core/auto_generated/layout/qgslayoutitemlegend.sip.in

@@ -67,6 +67,8 @@ The caller takes responsibility for deleting the returned object.
 
     virtual QIcon icon() const;
 
+    virtual QgsLayoutItem::Flags itemFlags() const;
+
     virtual QString displayName() const;
 
 

python/core/auto_generated/layout/qgslayoutitemmap.sip.in

@@ -41,6 +41,8 @@ Constructor for QgsLayoutItemMap, with the specified parent ``layout``.
 
     virtual QIcon icon() const;
 
+    virtual QgsLayoutItem::Flags itemFlags() const;
+
 
     void assignFreeId();
 %Docstring

python/core/auto_generated/layout/qgslayoutitempicture.sip.in

@@ -286,8 +286,6 @@ Forces a recalculation of the picture's frame size
 
     virtual void refreshDataDefinedProperty( QgsLayoutObject::DataDefinedProperty property = QgsLayoutObject::AllProperties );
 
-    virtual bool containsAdvancedEffects() const;
-
 
   signals:
     void pictureRotationChanged( double newRotation );

src/core/layout/qgslayoutitem.cpp

@@ -27,6 +27,7 @@
 #include "qgslayoutundostack.h"
 #include "qgslayoutpagecollection.h"
 #include "qgslayoutitempage.h"
+#include "qgsimageoperation.h"
 #include <QPainter>
 #include <QStyleOptionGraphicsItem>
 #include <QUuid>
@@ -123,6 +124,11 @@ int QgsLayoutItem::type() const
   return QgsLayoutItemRegistry::LayoutItem;
 }
 
+QgsLayoutItem::Flags QgsLayoutItem::itemFlags() const
+{
+  return nullptr;
+}
+
 void QgsLayoutItem::setId( const QString &id )
 {
   if ( id == mId )
@@ -326,6 +332,8 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
       drawFrame( context );
       p.end();
 
+      QgsImageOperation::multiplyOpacity( image, mEvaluatedOpacity );
+
       painter->save();
       // scale painter from mm to dots
       painter->scale( 1.0 / context.scaleFactor(), 1.0 / context.scaleFactor() );
@@ -854,7 +862,9 @@ void QgsLayoutItem::setBlendMode( const QPainter::CompositionMode mode )
 void QgsLayoutItem::setItemOpacity( double opacity )
 {
   mOpacity = opacity;
-  refreshOpacity( true );
+  refreshOpacity( mItemCachedImage.isNull() );
+  if ( !mItemCachedImage.isNull() )
+    invalidateCache();
 }
 
 bool QgsLayoutItem::excludeFromExports() const
@@ -870,12 +880,13 @@ void QgsLayoutItem::setExcludeFromExports( bool exclude )
 
 bool QgsLayoutItem::containsAdvancedEffects() const
 {
-  return false;
+  return itemFlags() & Flag::FlagOverridesPaint ? false : mEvaluatedOpacity < 1.0;
 }
 
 bool QgsLayoutItem::requiresRasterization() const
 {
-  return itemOpacity() < 1.0 || blendMode() != QPainter::CompositionMode_SourceOver;
+  return ( itemFlags() & Flag::FlagOverridesPaint && itemOpacity() < 1.0 ) ||
+         blendMode() != QPainter::CompositionMode_SourceOver;
 }
 
 double QgsLayoutItem::estimatedFrameBleed() const
@@ -1360,7 +1371,14 @@ void QgsLayoutItem::refreshOpacity( bool updateItem )
   double opacity = mDataDefinedProperties.valueAsDouble( QgsLayoutObject::Opacity, createExpressionContext(), mOpacity * 100.0 );
 
   // Set the QGraphicItem's opacity
-  setOpacity( opacity / 100.0 );
+  mEvaluatedOpacity = opacity / 100.0;
+
+  if ( itemFlags() & QgsLayoutItem::FlagOverridesPaint )
+  {
+    // item handles it's own painting, so it won't use the built-in opacity handling in QgsLayoutItem::paint, and
+    // we have to rely on QGraphicsItem opacity to handle this
+    setOpacity( mEvaluatedOpacity );
+  }
 
   if ( updateItem )
   {

src/core/layout/qgslayoutitem.h

@@ -287,6 +287,16 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
       UndoCustomCommand, //!< Base id for plugin based item undo commands
     };
 
+    /**
+     * Flags for controlling how an item behaves.
+     * \since QGIS 3.4.3
+     */
+    enum Flag
+    {
+      FlagOverridesPaint = 1 << 1,  //!< Item overrides the default layout item painting method
+    };
+    Q_DECLARE_FLAGS( Flags, Flag )
+
     /**
      * Constructor for QgsLayoutItem, with the specified parent \a layout.
      *
@@ -324,6 +334,12 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
     */
     virtual QString uuid() const { return mUuid; }
 
+    /**
+     * Returns the item's flags, which indicate how the item behaves.
+     * \since QGIS 3.4.3
+     */
+    virtual Flags itemFlags() const;
+
     /**
      * Returns the item's ID name. This is not necessarily unique, and duplicate ID names may exist
      * for a layout.
@@ -1109,6 +1125,7 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
 
     //! Item opacity, between 0 and 1
     double mOpacity = 1.0;
+    double mEvaluatedOpacity = 1.0;
 
     QImage mItemCachedImage;
     double mItemCacheDpi = -1;
@@ -1137,7 +1154,6 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
     void preparePainter( QPainter *painter );
     bool shouldDrawAntialiased() const;
     bool shouldDrawDebugRect() const;
-
     QSizeF applyMinimumSize( QSizeF targetSize );
     QSizeF applyFixedSize( QSizeF targetSize );
     QgsLayoutPoint applyDataDefinedPosition( const QgsLayoutPoint &position );
@@ -1157,6 +1173,8 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
     friend class QgsCompositionConverter;
 };
 
+Q_DECLARE_OPERATORS_FOR_FLAGS( QgsLayoutItem::Flags )
+
 #endif //QGSLAYOUTITEM_H
 
 

src/core/layout/qgslayoutitemlegend.cpp

@@ -64,6 +64,11 @@ QIcon QgsLayoutItemLegend::icon() const
   return QgsApplication::getThemeIcon( QStringLiteral( "/mLayoutItemLegend.svg" ) );
 }
 
+QgsLayoutItem::Flags QgsLayoutItemLegend::itemFlags() const
+{
+  return QgsLayoutItem::FlagOverridesPaint;
+}
+
 void QgsLayoutItemLegend::paint( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget )
 {
   if ( !painter )

src/core/layout/qgslayoutitemlegend.h

@@ -78,6 +78,7 @@ class CORE_EXPORT QgsLayoutItemLegend : public QgsLayoutItem
 
     int type() const override;
     QIcon icon() const override;
+    QgsLayoutItem::Flags itemFlags() const override;
     //Overridden to show legend title
     QString displayName() const override;
 

src/core/layout/qgslayoutitemmap.cpp

@@ -77,6 +77,11 @@ QIcon QgsLayoutItemMap::icon() const
   return QgsApplication::getThemeIcon( QStringLiteral( "/mLayoutItemMap.svg" ) );
 }
 
+QgsLayoutItem::Flags QgsLayoutItemMap::itemFlags() const
+{
+  return QgsLayoutItem::FlagOverridesPaint;
+}
+
 void QgsLayoutItemMap::assignFreeId()
 {
   if ( !mLayout )

src/core/layout/qgslayoutitemmap.h

@@ -71,6 +71,7 @@ class CORE_EXPORT QgsLayoutItemMap : public QgsLayoutItem
 
     int type() const override;
     QIcon icon() const override;
+    QgsLayoutItem::Flags itemFlags() const override;
 
     /**
      * Sets the map id() to a number not yet used in the layout. The existing id() is kept if it is not in use.

src/core/layout/qgslayoutitempicture.cpp

@@ -669,14 +669,6 @@ void QgsLayoutItemPicture::refreshDataDefinedProperty( const QgsLayoutObject::Da
   QgsLayoutItem::refreshDataDefinedProperty( property );
 }
 
-bool QgsLayoutItemPicture::containsAdvancedEffects() const
-{
-  if ( QgsLayoutItem::containsAdvancedEffects() )
-    return true;
-
-  return mMode == FormatSVG && itemOpacity() < 1.0;
-}
-
 void QgsLayoutItemPicture::setPicturePath( const QString &path )
 {
   mSourcePath = path;

src/core/layout/qgslayoutitempicture.h

@@ -259,7 +259,6 @@ class CORE_EXPORT QgsLayoutItemPicture: public QgsLayoutItem
     void recalculateSize();
 
     void refreshDataDefinedProperty( QgsLayoutObject::DataDefinedProperty property = QgsLayoutObject::AllProperties ) override;
-    bool containsAdvancedEffects() const override;
 
   signals:
     //! Is emitted on picture rotation change

src/plugins/georeferencer/qgsresidualplotitem.cpp

@@ -27,6 +27,11 @@ QgsResidualPlotItem::QgsResidualPlotItem( QgsLayout *layout )
   setBackgroundEnabled( false );
 }
 
+QgsLayoutItem::Flags QgsResidualPlotItem::itemFlags() const
+{
+  return QgsLayoutItem::FlagOverridesPaint;
+}
+
 void QgsResidualPlotItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget )
 {
   Q_UNUSED( itemStyle );

src/plugins/georeferencer/qgsresidualplotitem.h

@@ -30,6 +30,8 @@ class QgsResidualPlotItem: public QgsLayoutItem
   public:
     explicit QgsResidualPlotItem( QgsLayout *layout );
 
+    QgsLayoutItem::Flags itemFlags() const override;
+
     //! \brief Reimplementation of QCanvasItem::paint
     void paint( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget ) override;